Further reading...

Angostura Bitters

ANGOSTURA® aromatic bitters is a highly concentrated food and beverage flavouring. Made from a secret formula, it is a unique blend of natural herbs and spices which is used to flavour a wide variety of foods and drinks.
The "secret" was developed in 1824 by Dr. J.G.B. Siegert, a Surgeon General in Simon Bolivar's army in Venezuela. He used his aromatic bitters to improve appetite and digestive well-being of the soldiers. The word "Angostura" came from the town of that name in Venezuela where Dr. Siegert was based.
Angostura aromatic bitters is a unique flavour enhancer for food preparation, beverages and deserts; just a few dashes can enhance the flavour of any dish.
It is not bitter when added to food & drink, but rather has the ability to marry flavours, bringing out the best in them without masking their taste.
Source : http://www.angostura.com